Sheet diverters of all manner and variety are, of course, well known in the art. The same may range from the collating apparatus associated with an office copier, to sheet or web handling devices employed in the manufacture of paperboard articles, to sheet diverters specifically adapted to collate signatures in binding or otherwise assembling books, magazines or newspapers. Each of these environments presents a somewhat different challenge in designing an efficient diverter or collator, but the same objective tends to dominate the entire class of apparatus--accurately routing selected flexible webs or ribbon sections along a desired collating path to achieve the desired order of, e.g., pages is paramount.
In situations where the apparatus is of low or moderate speed, such as an office copier, design options are relatively straightforward. However, increasing speed has tended to be a limiting factor on the efficiency of sheet diverters or collators. Considering, for example, the physical qualities of paper or similar flexible webs moving at high speeds, relatively slight imperfections can be magnified, causing whipping, "dog-earring," or bunching of the paper web and ultimately contributing to a jam somewhere in the apparatus. Jams are cleared only by taking the device out of service and manually retrieving ruined product. The associated production delays and waste have severely handicapped the evolution of yet faster production techniques. For example, timing in a printing press operating at 700 to 800 feet per minute has proven to be readily achievable; conventional manufacturing techniques and tolerances are capable of providing accurate collation of signatures through sheet diverters and relatively reliable operation. The next incremental speed increase, to about 1,500 feet per minute, has been accomplished with some difficulty as rotational speeds rise and tolerances become significantly more important. Rotary elements moving at these higher angular velocities yield surface speeds at rotating rolls or cylinders which increase proportionately while inertial effects become quite pronounced. Tolerances must be held closely and timing controlled critically. The further advance to speeds over 2,000 feet per minute, and preferably over 2,500 feet per minute, is accompanied by the greatest of difficulties when all of these factors are borne in mind. To date, the art has not responded adequately to the needs for a sheet diverter which can efficiently collate signatures from a printing press at speeds in excess of 2,000 feet per minute while minimizing tendencies toward tearing or bunching of fast moving signatures and resultant machine jamming.
Other factors have also troubled the design of sheet diverters, particularly those employed in the printing industry. A conventional design which has thoroughly permeated the printing industry is a folder/sheet diverter which conveys signatures on a plurality of pins or other similar members which pierce the paper to grasp it and thence transport it throughout the apparatus. For most publications, with the exception of some newspapers, the marginal area through which the pins project must be trimmed as part of normal production techniques. On the one hand, this creates an additional manufacturing step and contributes to increased costs of production; on the other hand the approximately 1/4 inch strip cut from the bound signatures is waste which is costly in terms of the added expenses of procurement and disposal. Consequently, the art has sought to provide so-called pinless folders which overcome those historical problems. A certain level of success has been achieved considering designs which operate well at the lower press speeds, for example, less than about 1,000 feet per minute. At higher speeds the problems summarized above begin to dominate the situation. Particular shortcomings may be noted for pinless folders which ar pushed to operate at speeds perhaps beyond their design limits where there is a lack of structure or other functional provision to ensure positive control and transport of the signature as it progresses through the stations of the folder/diverter/collator. That function, formerly provided by the pins pierced through the web to restrain it during its travel, is an important one not fully accommodated by many commercial pinless folders.
An interesting diverter design is disclosed in U.S. Pat. No. 4,373,713. The diverter mechanism is comprised of a pair of counterrotating diverter rolls bearing specifically configured camming surfaces cooperating with a diverter wedge or plate disposed immediately downstream of the nip created by those rolls. That wedge, in the nature of a triangular member, defines two paths, one of each along the angled surface from its apex. As a signature reaches the nip of the cooperative diverter rolls it will encounter a cam surface on one or the other which will direct the leading edge of the signature to one or the other side of the diverter wedge. Programming capabilities may be achieved by the user to select, for example, two signatures for diversion on one side of the wedge and then one on the other, by judicious placement and design of the camming surfaces.
High speed operation of a diverter mechanism such as that disclosed in the '713 patent is problematic. The raised cam elements at the outer periphery of the rotating rolls will tend to cause vibration as the angular velocity of the rolls increases to the realm of interest with regard to the sheet speeds (surface velocities) anticipated by the present invention, up to about 2,500 feet per minute. While, of course, the rotating rolls can be counterbalanced for dynamic operation, it is not at all clear that the design would tolerate those types of speeds even under the best of circumstances and efficiently divert the fast-moving signatures into one or the other of the desired collation paths. In short, that approach is not viewed as workable in light of the high speeds sought to be attained nor is it seen to be particularly reliable in reducing jamming tendencies which are expected to arise in these settings.
A conceptually similar design, albeit for substantially lower speeds and different types of materials, is the one found in U.S. Pat. No. 3,391,777. That device is tailored to divert flexible batts such as those utilized in the manufacture of disposable diapers or sanitary napkins. The batts are confined between pairs of belts moving toward a rotating disc having a generally semicircular "cam" surface. The disc is thus composed of a first segment of a short radius and a second segment of a large radius. Two deflection paths are associated with the moving disc which directs first one batt and then the next to one of the two paths; a first path is provided coincident with the shorter radius while a second path is provided coincident with the larger radius. Coordinating the rotational speed of the disc with the linear travel of the belts and batt, the leading edge of the latter will encounter the surface corresponding to one or the other of the radii and be directed to the corresponding path. This diverter, like the one mentioned above, is limited in its applicability to collate flexible web members as speeds increase substantially.
U.S. Pat. Nos. 3,218,897 and No. 3,565,423 are of background interest insofar as each concerns apparatus for conveying and stacking flexible sheets such as paper sheets. Each of the apparatus disclosed in those patents includes a diverter gate or the like which controls the direction of paper flow along one of two paths. A principal path is fed while means are provided to scan or otherwise examine the paper. In the event a defect is detected requiring rejection of a sheet, the diverter gate is activated and directs that sheet along a second path.
The blanking machine of U.S. Pat. No. 2,164,436 is of general interest for its disclosure of a distributing roll set for directing components in the blanking of a paperboard box. Aligned notches in deflecting discs receive cards and distribute them along separate paths. Each of the discs is eccentrically notched or shouldered and carries a cam finger. As the distributing rolls rotate, the cam finger of one roll will always be presented to the notch of the opposing roll, thus deflecting successive blanks first upwardly and then downwardly from the horizontal plane of the line of bight between the rolls. The upward or downward course thus initiated is maintained by a wedge-shaped deflector, disposed with the apex directed into the bight between the rolls; the downwardly deflected blank must pass beneath the wedge while the upwardly defected blank must pass above it. Once again, the depending structure, in this case the cam finger, precludes attainment of substantial speeds under reliable and efficient conditions.
From the foregoing, it is evident that the art has yet to respond with a pinless folder/sheet diverter capable of operating in concert with a high speed press at paper speeds significantly in excess of 2,000 feet per minute and reaching 2,500 feet per minute or more. Thus, the need for such a device is a felt one, to which the present invention responds.